Water is an important kind of natural resource in people's life. People cannot live without water. With the development of modern society, shortage of water resource is becoming increasingly severe, and water saving has become a topic of great concern. When water is used in daily life, water supply system is established with water supply circuits, and switching valves are disposed at water circuit terminals to control water flow. Under such circumstances, valves at water circuit terminals need to bear certain water pressure, and if a valve is damaged, the water in it will rush out, causing huge amount waste of water resource. If not handled timely, this will not only lead to huge amount waste of water resource, but also cause damage to other assets.
In circuits of natural gas, some relieve valves for overload protection are designed to prevent damage caused by leakage. For instance, Chinese patent CN2615459Y disclosed a relieve valve for overload protection for compressed natural gas circuit, comprising a joint, a valve body, a valve spring, and a valve mandrel. A hollow joint is screwed into the lower end of the valve body through a female screw, a cylindrical cavity is formed at the middle of the valve body, a valve mandrel with air holes thereon is disposed in the cylindrical cavity, a conical valve seat is disposed above the valve mandrel, a valve spring is sleeved on the valve mandrel, and overflow holes are disposed on the upper part of the valve mandrel; coaxial circular venting grooves and hollow slots perpendicular to the same are disposed on the upper section of the cylindrical cavity, repositioning venting bolts are mounted in the circular venting grooves, and screw threads are set on the outer surface of the hollow slots. This relieve valve for overload protection, when its corresponding pipeline is ruptured or damaged, is able to close the gas outlet automatically according to the gas flow rate and differential pressure, so as to prevent leakage of high pressure gas, increase safety level in use, and reduce accident loss. However, while this kind of valve is applied in water circuit, a relatively high pressure is generated by water at one end of the valve mandrel when the valve is opened, because water is in its liquid state and does not diffuse as fast as high pressure gas, and this pressure cannot be released as the overflow holes are relatively small, so that the valve mandrel is apt to move upward as a result of the water pressure, thus blocking the outlet. Therefore, this valve is not suitable for being applied in water circuit control. Besides, after the valve mandrel blocks the outlet, the pressure is mainly concentrated at the top of the valve mandrel with a relatively small area of stress, this may provide enough force in high pressure gas circuit, however, in normal water circuit, because of the relatively small area of stress, the force provided is relatively weak, thus cannot seal the outlet firmly, and the reliability of the system is decreased.